There are many challenges in predicting the fate of inhaled particles in the lung and to determine the influence of formulation and device factors on the efficacy and safety of orally inhaled drug products. In this proposal, we seek to develop a in vitro dissolution system, which can predict clinically related endpoints such as the rate and extent of drug absorption measured by pharmacokinetics. The major research objective is to develop a robust dissolution system which takes into account the composition and limited lung fluid available for dissolution, influence of local dosimetry differences between formulations and devices and how these factors influence dissolution and permeability of drugs for delivery to the respiratory tract. A greater understanding and IVIVC mathematical modeling of the relationship between the physico---chemical properties of drugs, local dissolution effects and permeability will provide the necessary science and tools to enable greater control of product safety, efficacy, potency, quality and functionality. The exploration into the relationship between dissolution, permeability and pharmacokinetics will enable the FDA to direct both branded and generic industries to define quality and functionality of orally inhaled drug products.